Signaling system



D. E. FOSTER SIGNALING SYSTEM Oct. 26, 1937.

Filed June 2, 1934 Patented Oct. 26, 1937 UNITED STATES 7 2,096,800SIGNALING SYSTEM Dudley E. Foster, Evanston, 111., assignor, 'by mesneassignments, to Reconstruction Finance Corporation, Chicago, 111., a,corporation Application June 2, 1934, Serial No. 728,699

Claims.

My invention relates in general to electronics and has more particularreference to electron flow control by means of negative bias in anelectron flow circuit, the invention having particular ap- 5 plicationin the automatic control of sensitivity in electrical transfer systems,7 more especially radio receivers.

An important object is to provide, in an electron flow circuit, meansfor normally establishing an electron flow of constant character and forvarying the electron flow in response to variations in strength of anelectrical potential impressed upon the circuit, a further object'beingto accomplish the control automatically and a still further object beingto provide for electron flow control only after the impressed potentialexceeds a predetermined value. Another object is to utilize a powersource for normally applying a bias upon an electron flow circuit so asto induce, normally, an electron flow of substantially constantcharacter in said circuit and to utilize the same power source toprovide for automatic control of the electron flow whereby to maintainconstant the energy output of the system in response to energy deliveredto the system at a varying rate.

Another object is to provide an electrical transfer system, moreespecially a radio receiver, having means normally operable to cause thesystem to deliver a signal, corresponding in strength to the strength ofa signal applied in the system, and also operable, after the strength ofthe applied signal exceeds a predetermined value, to automaticallycontrol the system, in accordance with the instantaneous amount ofenergy delivered thereto, so that the system may deliver energy at auniform rate even though the amount of energy delivered to the systemmay fluctuate; a further object being to accomplish the foregoing bybiasing'the transfer circuit and more particularly by a normal orinitial bias of constant character and a delayed bias of fluctuatingcharacter, and to produce both the initial bias and the delayed, orautomatic electron flow control, bias from a common source of biasingpotential.

Among the other important objects and advantages of my present inventionis to utilize an electron flow device suchas a diode to produce, forbiasing purposes, unidirectional potential fluctuating in proportion tothe strength of a signal impressed upon said system and to apply saidpotential to variably bias an amplifier forming a part of said systemand thus control signal amplification; to utilize an initial bias ofsubstantially constant value to delay the application of the fluctuatingbias until the strength of the impressed signal exceeds a predeterminedvalue; to maintain at substantially uniform strength,

signals, delivered to an electrical signal transfer 0 system, such asa'radio receiver; to prevent aping any vibration of'the 'frequencyorderwhich it is desired to exclude; to control the bias applied to theamplifier of a signal transfer system,

such as a radio receiver, in proportion to variations in the energy ofthe applied signal as, for example, duringfading; to arrange thecondenser, which accomplishes: the control during fading, so as tomaintain its charge'during vibrations having higher than the fadingfrequency accommodatedand thus prevent alteration of the bias applied tothe amplifier in response to normal audio or radio frequency componentsof the applied signal; to arrange the alternating current and fadingfrequency control means in 'cascade form when applying the same in asystem having more than one stage of amplification'so that the filteringaction on the biasing potential applied to an earlier stage ofamplification will be greater than that on the biasing potential appliedto a later stage in order to provide'a filtration safety factor for thebiasing potential applied to the initialamplifying stages, to separatethe stages and prevent inter-action there- V between; and to improve theoperation of the i bias-applying circuit in response to fading; to

utilize, in a signal transfer system, a condenser,

in parallel relationship with an electron flow device, such as a diode,operating as'a detector, and so proportioned'that the voltage developedacross the resistance, by the operation of the electronv flow detector,will 'be maintained substantially constant during a relatively highfrequency or super audio vibration, the resistance and condenser,however, being proportioned to permit discharge of the condenser andconsequent reduction of the voltage developed across the resistanceduring any relatively low frequency vibration so as to vary thepotential across the resistor in accordance with the fluctuations in thelow frequency vibrations impressed thereon to permit the circuit tofunction as a detector; to utilize capacity reactance in combinationwith an electron flow device, in a translation system, to detect acomponent of predetermined frequency in a modulated or composite waveimpressed upon the system; to detect a component of predeterminedfrequency in a composite Wave containing said component by controllingthe potential developed in an electron flow device on which thecomposite wave is impressed.

These and numerous other objects, advantages, and inherent functions ofthe invention will become apparent as the same is more fully understoodfrom the following description, which, taken in connection with theaccompanying drawing, disc-loses signal transfer systems embodying myinvention.

Referring to the drawing:

Figure l is a diagrammatic representation of a signal transfer systemembodying my present in- V vention.

Figure 2 is a diagrammatic view showing how resistance and capacity inthe bias-applying 'circuit may be arranged in cascadein order to afforda greater filtering effect upon the biasing potential applied to anearly stage of amplification than upon the biasing potential. applied toa later stage.

Figure 3 is a diagrammatic View showing'the electron flow device, whichdevelops the biasing potential, connected in the system substantially inadvance of the detector in order to preserve the apparent selectivity ofthe system.

Figure 4 shows how the detector and bias po tential producing elementsmay be combined.

'To illustrate my invention, I have shown a signal transfer systemcomprising a plurality of electron fiow devices including an initialamplifier element II, a second amplifier element I3, a detector elementI5, a bias potential developing element I1, and means interconnectingsaid elements to form a signal transfer system.

Each of the elements II, I3, I5, and I! comprises an electron emittingdevice or cathode I9, which, in the illustrated embodiment, comprises afilament. The filaments may be energized for electron emission in anysuitable fashion, as by connecting the same with a source of electricalpower. The cathodes I9 also are preferably grounded, which, as shown inFigure l, is accomplished by connecting the same to a common. groundedconductor 2I.

Each of the: elements II, I3, I5, II, respectively, has a plate or anodeI2, I4, I5, and I8, and the amplifying elements II and I3 are alsoprovided each respectively with grids 23 and 25 to which negative biasmay be ap plied in accordance with the teaching of my present invention.The amplifier elements II and I3 may be coupled together and to thedetector element I5 and to the antenna or signalreceiving element 21 inany suitable fashion, but I have, for the sake of illustrating myinvention, shown coupling means comprising transformers 28, 29, and 30,which are shown as radio frequency transformers, since the amplifiers IIand I3, in the illustrated embodiment, are radio frequency amplifiers.It will, however, be understood that the principles of the invention arenot necessarily restricted to radio frequency amplification.

To apply the signal to the transfer system, the antenna 21 is connectedto one end of the primary winding 3| of the transformer 28, the oppositeend of which primary winding is grounded.

One end of the secondary winding 33 of the transformer 28 is connectedto the grid 23 of the initial amplifier element I I, the opposite end ofsaid secondary winding being connected through a resistance 35 and aresistance 3! to the negative side of a direct current power source 39,the positive side of which is connected to the grounded conductor 2?. Atuning condenser 4| is prefer-. ably connected between the opposite endsof the secondary winding 33.

The plate I2 of the element II is connected to one end of the primary 5|of the transformer 29, the opposite end of said primary winding beingconnected through suitable direct current, plate potential, power sourceand thence back to the cathode of the amplifier element II. thesecondary winding 53 of the transformer 29 is connected with the grid-25 of the second amplifier element I3, the opposite end of saidsecondary winding being connected through the resistance 35 and theresistance 31 to the negative side of the power source 39; A tuningcondenser GI is preferably connected between the opposite ends of thesecondary winding 53. The circuits, from the power source 39, to thegrids of the amplifier elements II and I3, through the resister 35 andthe control resistor 31, comprise bias potential applying circuits, anda condenser is connected between the grounded conductor 2I andpotential-applying circuits, at a point between the resistor 35 and saidgrids, for a hereinafter more fully explained.

connected to one side of the primary winding ii of the transformer 30,the opposite end of said primary winding being connected through a suit-One end of 1e plate M of the second amplifier element I3 able directcurrent, plate potential, power source, 7

and thence back to the cathode of the amplifier element 53. The;secondary winding 13 of the transformer 35 forms the input to adetecting circuit, one end of said winding being connected to the plateI3 of the detector element I5, the opposite end of said secondarywinding I3 being connected to the grounded conductor 2| through a.resistance-capacity net work I5 comprising a resistor Ill and condenserI9 arranged in parallel relationship. A tuning condenser 8i is connectedbetween the opposed ends of the secondary windin i3, and an outputconnection 83 is provided in the detecting circuit between the secondarywinding and the net work 15. The secondary winding 53 and its associatedcondenser 8|, the net work and the element I5 are thus associated toform a detector circuit, the function of which I shall hereinafterdevelop more fully.

The plate I8 of the automatic bias potential developing unit I l is ormay be connected through a condenser 55 to the detector circuitanywherebetween the plate I6 of the detector element I5 and the winding73. The plate I8 of the unit I? is also connected by means of aconductor 5! through the resistor 31 to the negative side of the powersource 39, so that the unit I! is also connected to the potentialapplying circuit which extends to the grids of the amplifier elements.

A signal, impressed on the antenna, is transferred progressively throughthe amplifiers II and I3, it being understood that any number ofamplifier units or stages may be utilized, the signal passing to thedetecting circuit through the transformer 30, and the detected signal istransferred to the output through the terminal 83.

The function of the net work 151s to provide for automatically biasingthe detector element I5,

when the signal system is functioning, in order to maintain a constantoperating potential between its anode and cathode. To this end, theresistance 11 and condenser 19 are proportioned so that the condenserwill not discharge through the resistor to any great extent during anyradio frequency cycle in order thus to maintain the voltage across theresistance 11 substantially at its peak value as long as the detectingcircuit is subjected to radio frequency impulses, such as the carrierwave of a signal, impressed on the cir-' cuit through the transformer30, wherebyto maintain a constant operating potential across theresistance 11 during the time of the cycle of a radio frequency waveimpressed on thecircuit. The condenser 19, however, is arranged todischarge substantially completely during the time of the cycle of anaudio frequency component of the wave impressed on the net work so thatthe voltage across the resistance 11 will follow the variations of theaudio component of the signal, and will thus accomplish diode detectionsubstantially without distortion.

One of the objects of my present invention is to provide for increasingtheamplification, accomplishedupon thesignal by the-elements H and I3,inversely in proportion to the strength of the signal impressed upon thesystemat the antenna. This is accomplished by means of the potentialdeveloping element 11, the power source 39 and resistance 31 and theconnections extending through the resistance 35 to the grids 23 and 25of the elements I I and I3.

It will be noted that the anode and cathode of the element 11 are in apotential developing circuit including, in series, the resistor 31, thedirect current source 39, and the conductors 21 and 51. The plate oranode 18 of the element 11 also is connected through the condenser 55 tothe detector circuit. Consequently, the signal applied to the detectorcircuit is also applied to the element 11. The application of the signalin this manner to the plate of the element 11 permits various currentsto flow in the potential developing circuit and the voltage across theresistor 31, due to these currents, includes a direct current voltageproportional to the signal strength, an alternating current voltagecorresponding to the audio modulation of the carrier wave of the signaland an alternating current voltage corresponding to the carrier waveitself. The direction of the direct current component is such that theend of the resistor 31, remote from the power source 39, tends to becomenegative with respect to its end which is connected to the power source.The negative condition of the remote end of the resistor 31 increaseswith increase in signal strength impressed upon the system. Since the,grids of the amplifier elements I! and 13, are connected to the remoteor negative. end of the resistor 31, it will be seen that the grids areat the same negative potential with respect to ground as is said remotenegative end of the resistor 31. The resistor 35, which is in serieswith the grids does not afiect this condition, and the condenser 59 nor?mally prevents any direct current from passing to ground, withconsequent loss of biasing potential at the grids.

It will be noted that my invention provides for the application ofuniform negative bias on the amplifier tubes during the interval whilesignal strength is increasing, as during tuning of the set, to the pointwhere automatic control is needed. Thisinitial negative biasisaccomplished directly by the power source 39 operating through tial, theamount of which depends upon the voltage available at the power sourceand the amount of resistance supplied by the resistors 35 and 31, isapplied to the grids. The arrangement also provides for the delayedapplication of the auto:

matic sensitivity control effect, which becomes effective only after thestrength of the signal-de-;

livered at the output reaches the full volume at which the system isdesigned to operate. The power source 39 is so connected that a negativepotential is app-lied to the plate of the element l1 through theresistor 31, and untilthe signal reaches a strength suflicient toestablish a negative condition at the plate in excess of thatapplied bythe power source, the bias applied on the grids of the amplifiers willremain constantat the value determined by the power source. It is onlyafter the strength of the signal increases sufiiciently to develop anegative condition at the plate greater than that afforded by the powersource, that the bias on the amplifier grids commences to vary inorderto accomplish automatic volume control.

As the signalstrength increases above that -nec'-' essary to make theplate-of the element I1 more negative than the power source 39, theremoteend of the resistor 31 and'therefore thegrids of'the amplifierelements H and 13 will become r'n'ore negative with respect to ground.Consequently, the negative bias applied to the grids will increase asthe signal strength increases, and the amplifying efiiciency of theelements 'I I and 13 will be decreased in proportion to the increase insignal strength and vice versa. By selecting the proper amounts ofresistance for the resistors 35 and 31, the strength of the signaldelivered at the output 83 may be made substantially uniform al thoughthe strength of thesignal' applied to the system at the antenna variesover a wide range. It should benoted that the same power source providesboth the initialbias and the delayed automatic control which results inconsiderable economy of parts, since it is unnecessary to provideseparate, power sources for applying the'initial bias and for effectingthe automatic delayed control; Furthermore, the-automatic sensitivitycontrol effected is more uniform so that the signal delivered at theoutput is of substantially constant strength.

It is desirable to prevent all of the alternating current potentialcomponents, 'developed'in, the element 11, from reaching the grids ofthe amplifiers II and 13. If a radio frequency component is permitted toreach the amplifier grids, the entire system will be caused to oscillateand if an audio frequency component reachesthe grids, V

the strength of the signal delivered at the output of the system may becaused to fluctuate at audio frequency which, of a course, isundesirable." l1 prevent these alternating current components fromreaching the amplifier grids by nieansof the resistance 35 and thecondenser 59, which coopcrate to form'a filter to remove the undesiredcomponents. The resistor-35 and the condenser 59 are so proportionedthat the condenser will not discharge during an audio or radio"frequency cycle, but will maintain the voltage applied to'the gridsconstant during such an interval. The con tioned so that the former willdischarge during fading, which causes the applied bias potential to varyduring fading to the end so that amplification will be varied inaccordance with fading so as to maintain the'signal strength at theoutput during such intervals without distortion.

the resistors 31 and 35 whereby a negative poten denser 59 andresistance 35, however, are propor passes only through the resistorsection 234.

this arrangement also the function of. the condenser 59 is accomplishedby means of two condensers 60, one of which is connected between groundand the grid circuit of the element ll, while the other is connectedbetween ground and the grid circuit of the element I3., I thus dividethe resistance 35 and condenser 59. into a cascade arrangement in orderto vary the alternating current filtration accomplished upon the biasingpotential delivered to the several amplification elements to the endthat the filtering effect performed upon the biasing potential deliveredto the initial element l I will be greater than the filtrationaccomplished upon the biasing potential delivered to the other amplifierelement 13. This is desirable since permissible distortion in theinitial amplifying element is; much less than the permissible distortionin the other elements, since a given distortion, in the initialamplifier is amplified to a greater degree and results in greaterdistortion in the signal delivered at the output than is the case when asimilar degree of distortion occurs in the later amplifier.

Another advantage derived from cascading the resistance 35 and condenser58 resides in the separation of the amplification stages, thusaccomplished, which prevents inter-action between the stages. Thecascade arrangement also affords more accurate and sensitive response tofading in the system since the condensers 59 may be selected todischarge with greater accuracy during fading than can the singlecondenser 59 arranged to serve a plurality of amplifier elements. By thesame token, the cascade arrangement of resistance and capacity in thegrid bias:

ing circuit may be arranged to diiTerentiate-more exactly between theattenuation applied in filtering the audio and radio frequencycomponents delivered by the element ll at the remote end-of the resistor31 and the preservation of voltage desired during fading.

By connecting the plate of the potential generating element I! throughthe condenser 55 to the detecting circuit, the relative selectivity ofthe detector and automatic volume control diodes is made more uniform,which makes it more diflicult to tune the set properly to the carrierfrequency of an applied signal. During tuning, the signal strength doesnot abruptly increase to its maximum value as the system reaches tunedcondition, but the signal strength increases gradually to a maximum sothat it is difficult to'determine exactly when the system is properlytuned- This is because the automatic sensitivity control causes the gridbias to vary in accordance with signal strength in such a way as to tendto keep'the output uniform. The grid bias, in the system shown in Figure1, is proportioned to the signal strength in the detector circuit.Consequently; the output energy of the detector circuit is made moreuniform not only during the operation of the system in tuned condition,but also during tuning. By connecting the plate l8 of the element I!through the condenser 55 to a point in the amplifying system by means ofa conductor 20 as shown in Figure 3, instead of to the detectingcircuit, as shown in Figure 1, the selectivity of the detector circuitmay be utilized to improve the apparent selectivity of the system duringtuning without impairing the automatic control features, since, by soconnecting the element [1, the selectivity of the detecting circuit maybe preserved unaffected by the automatic volume control action for usein tuning, which is not the case where the element I1 is connecteddirectly to the detector circuit. Y

It is also possible to combine the elements; l5 and IT as shown inFigure 4 by providing a single element 63 having a filament or cathodel9 and two anodesor plates, one l6 of which is connect-.. ed in thedetector circuit to perform the functions of the plate of the detectorunit, while the'other I8 is connected through the resistor 31 to thenegative side. of the power source 39 and serving the function of thebiasing potential generating element ll, said plate [8 being alsoconnected through a condenser 55 either to the detector circuit or toone of the earlier amplifier stages, as indicated-in dotted lines inFigure 4. r a

It is thought that the'invention and numerous of itsattendant advantageswill be understood" construction, and arrangement of the several partswithout departing from the spirit or scope of my invention orsacrificing any of its attendant advantages, the forms herein describedbeing preferred embodiments for the purpose. of illustrat ing myinvention.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is as follows:

i. A signal transfer system comprising signal input and output means, anelectron flow device including a control element and control means'fordeveloping a fluctuating biasing potential proportional to the strengthof the signal impressed on the system throughsaid input means, and forapplying said fluctuating potential upon the control element in order tomaintain the signal, delivered at the output means, at substantiallyconstant strength regardless of fluctuations in signal strength appliedto the system'through the input means, said control means comprising aconstant potential source of electrical energy connected to apply asubstantially constant biasing potential on the control element, adetector element operatively associated with said transfer system andcapable of developing a negative potential of magnitude corresponding tothe signal strength impressed on said system through said input inputmeans, means for applying said developed potential to the controlelement of the. electron flow device, whereby to maintain the. signal,delivered at the output, at substantially constant strength regardlessof fluctuations in the strength of the signal applied to the system, anda source of electrical negative potential connected to thecontrolelement to apply a constant negative bias of predetermined valueon the control element, said detector means and said power source beingconnected together in parallel whereby a constant bias will be appliedon said control element as long as the fluctuating potential developedby the detector means has a value less than that maintained on thecontrol element by said source, said fluctuating developed potentialbecoming effective as an automatic control on said control element onlyafter the developed potential exceeds that maintained on the controlelement by said power source.

3. A signal transfer system comprising signal input and output means,and a plurality of electron flow devices each having a control elementand the several electron flow devices being con- I nected in cascadearrangement between the input and output means to form successive stagesof amplification in said system, means operatively associated with saidtransfer system for developing a fluctuating biasing potentialinstantaneously proportional to the signal strength impressed on thesystem through said input means, a source of constant biasing potentialconnected in parallel with respect to the potential developing means,and circuit means to apply the developed fluctuating potential and theconstant potential together on the control elements of the severalelectron flow devices whereby a constant bias is normally applied onsaid control elements as long as the fluctuating potential is lower thanthat applied by said source, the fluctuating bias being applied onlyafter the developed potential exceeds that provided by saidsource.

4. A signal transfer system comprising signal input and output means,and a plurality of electron flow devices each having a control elementand the several electron flow devices being connected in cascadearrangement between the input and output means to form successive stagesof amplification in said system, means operatively associated with saidtransfer system for developing a fluctuating biasing potentialinstantaneously proportional to the signal strength impressed on thesystem through said input means, a source of constant biasing potentialconnected in parallel With respect to the potential developing means,and circuit means to apply the developed fluctuating potential and theconstant potential together on the control elements of the severalelectron flow devices whereby a constant bias is normally applied onsaid control elements as long as the fluctuating potential is lower thanthat applied by said source, the'fluctuating bias being applied onlyafter the developed potential exceeds that provided by said source, thebias being applied on said control elements through individual biasapplying circuits in relatively parallel arrangement and differentialfiltering means in the several bias applying circuits whereby the 7associated with said transfer system for develop-,

ing a fluctuating biasing potential instantaneously proportional to thesignal strength impressed on the system through said input means, asource of constant biasing potential connected in parallel With respectto the potential developing means, and circuit means to apply thedeveloped fluctuating potential and the constant potential together onthe control elements of the several electron flow devices whereby aconstant bias is normally applied on said control elements as long 'asthe fluctuating potential is lower than that applied by said source, thefluctuating bias being applied only after the developed potentialexceeds that provided by said source,the bias being applied on saidcontrol elements through individual bias-applying circuits in relativelyparallel arrangement and difierential filtering means in the severalbias applying circuits whereby the potential applied to the controlelement of an electron flow device, comprising an advance stage ofamplification, is subjected to a relatively greater degree of filtrationthan is applied to the biasing potential delivered on the controlelement of an electron flow device comprising a later amplificationstage of said system.

DUDLEY E. FOSTER.

